The U.S. Renewable Fuels Standard (RFS) mandates the production of 16 billion gallons of lignocellulosic biofuels (primarily EtOH) by 2022. Subsumed with this mandate is the inevitable availability of an enormous amount of lignin as a co-product of biofuel manufacture. Assuming that a commercial biorefinery produces 80 gallons biofuel/ton biomass and that the biomass averages 20% by weight lignin; operation at the legislated levels of the RFS will afford 40 million tons of lignin on an annual basis. This remarkable level of renewable carbon production and availability is an attractive target for downstream chemical processing and conversion to higher value materials. However, the heterogeneous structure of lignin has frustrated efforts to selectively convert this abundant biopolymer into low molecular weight aromatics. Moreover, the structure of lignin is variable. The distribution of substructural units within isolated lignin is a function of both the lignin source and the methodology employed in its isolation. Lignin possesses a network of alkyl chains linking the aromatic network together.
A few reports on lignin oxidations are available where either enzymes or complex catalytic systems such as perovskite-type oxides are used, with a variety of benzylic oxidation procedures are available where stoichiometric or catalytic amounts of reagents. However, in most of these reactions, hazardous, expensive and toxic heavy metals may be required. Further, most of these procedures are specific to a very small number of substrates. There exists therefore, a simple catalytic oxidation that can oxidize a wide range of lignin compounds to corresponding carboxylic acids.